For over a century, wallboard has been used as an interior wall covering. The most common type of wallboard is gypsum wallboard. The basic construction includes a core of cementitious gypsum that is positioned between two opposing paper liners. One of the paper liners forms the exterior wall finishing. An example of a paper-covered gypsum board is illustrated in U.S. Pat. No. 2,806,811 to Von Hazmburg. Von Hazmburg discloses a board that primarily consists of a thick gypsum core that is encased in a fibrous envelope consisting of both a manila sheet and a newsprint sheet. These sheet layers can be made from a conventional multi-cylinder paper making process.
It is also known to replace the paper facing sheets with opposing glass fiber mats. This construction is referred to as glass reinforced gypsum boards (or “GRG”). A GRG board is disclosed in U.S. Pat. No. 4,265,979 to Baehr et. al. A further improvement was realized by slightly embedding one or more of the glass fiber mats into the core slurry of the board during the manufacturing process. This results in a thin film of slurry being formed on the outer surface of the board. Building boards with this construction are referred to as embedded glass reinforced gypsum (EGRG) boards. EGRG boards eliminate, or greatly reduce, the presence of exposed fibers.
Yet, paper faced boards, GRG boards, and EGRG boards, all require extensive finishing materials and labor intensive steps in order to achieve a desirable exterior wall finishing. According to the Gypsum Association, wall finishings are measured on a scale ranging from the least smooth (Level 0) to the most smooth (Level 5). A level 0, the exterior surface of the board is rough and or textured in appearance. Contortions and undulations are easily visible upon the board. At Level 5, the exterior surface of the board has a very smooth appearance that approximates glass.
Paper faced gypsum board is not capable of yielding a Level 5 finish without the incorporation of special sealers and multiple skim coats of a finishing compound. Sanding is also required as each level is built up. Hence, achieving a Level 5 finish with paper faced boards is a labor intensive process that requires a variety of added materials.
Forming a Level 5 finish on GRG or EGRG boards can prove equally problematic albeit for different reasons. GRG and EGRG boards have a cementitious surface and/or core that is filled with desiccant-like materials. Thus, when finishing compounds are added to the surface of these boards, they are quickly absorbed. To be effective, large volumes of finishing compounds must be used. The absorption of the finishing compounds can also cause voids, cracking, premature desaturation and resultant quick set. All of these precludes the formation of a Level 5 finish on GRG or EGRG boards.
Various efforts have been made over the years to reduce the materials, labor, and time needed to adequately finish the exterior surface wall boards. For example, sprayable compounds have been developed to provide wall boards with Level 4 or Level 5 finishes. Yet, these sprayable compounds suffer from all of the aforementioned drawbacks. Paper faced boards do not saturate quickly enough. As a result, sprayable finishes run when applied to paper faced boards. By contrast, glass reinforced boards absorb liquids too quickly. As a result, unnecessarily large volumes of spray must be used in order to achieve a desired finish. These problems can only be overcome by using skim coatings or specialized primers, which only adds to the time and expense of the finishing effort.
The composite building boards of the present disclosure are designed to overcome these drawbacks by utilizing a polyester film to achieve a smooth exterior finish with minimal finishing materials, time or expense.